1. Field of the Invention
The present invention relates to a method of truing a grinding wheel formed from super hard abrasive grains which is used in a grinding apparatus.
2. Discussion of the Prior Art
Truing of a grinding wheel formed from super hard abrasive grains, such as a CBN (Cubic Boron Nitride) grinding wheel, is effected by traverse-feeding a rotary truing tool or a pyramidal single- or multiple-diamond truing tool along the cutting face of the grinding wheel.
In the case of a grinding wheel formed from super hard abrasive grains such as a CBN grinding wheel, the level of grinding force of the grinding wheel immediately after it has been trued is greatly different from that immediately before the grinding wheel was trued. The level of grinding force of the grinding wheel immediately after truing is relatively large, but as the grinding wheel is used to grind workpieces, that is, as the stock removal increases, the level of grinding force decreases and eventually reaches a steady state. More specifically, immediately after truing, the amount by which abrasive grains project from the bond on the outer peripheral surface of the grinding wheel is relatively small, and the cutting edge defined by the distal ends of abrasive grains is dull. For these reasons, the cutting ability of the grinding wheel is inferior and the level of grinding force is therefore high. On the other hand, as the grinding operation progresses, chips generated as a result of the grinding remove the bond between abrasive grains to define chip pockets, and the cutting edge defined by the distal ends of abrasive grains is sharpened as a result of the grinding operation, resulting in a lowering in the level of grinding force.
Accordingly, it is necessary to lower the level of grinding force immediately after the grinding wheel has been trued. It may be possible to meet this requirement by increasing the infeed of the truing tool with respect to the grinding wheel.
The above-described solution to the problem suffers, however, from the following disadvantages. As the infeed of the truing tool is increased, a sharper cutting edge is formed on the grinding wheel and therefore the level of grinding force may be decreased as shown by the solid line in FIG. 5. However, if the grinding wheel has a deflection, the deflection cannot be removed even by carrying out truing many times with a large infeed. Instead, as the infeed of the truing tool is increased, the deflection of the grinding wheel grows as shown by the chain line in FIG. 5. This is attributed to the fact that, as the infeed of the truing tool is increased, the frequency by which the cutting edge of the truing tool becomes worn increases and the truing tool is undesirably moved from its cutting position due to the resistance occurring during truing.